Rotor pair for positive fluid displacement

ABSTRACT

The rotors of a pair have intersecting axes. Their intermeshing teeth have tooth numbers differing by one and are deep enough to contact all around the rotor periphery. The entire tooth surfaces of one rotor are formed conjugate to the tooth ends of the other rotor. Said tooth ends have convex profiles in planes perpendicular to the tooth direction. The curvature centers of said profiles are displaced from the pitch surface towards the tooth bottom, so that the tooth addendum is algebraically smaller than the curvature radius of said end profile. Preferably said tooth ends are applied to the larger rotor of the pair, and may have a constant profile all along the tooth length.

United States Patent [191 Wildhaber Dec. 24, 1974 ROTOR PAIR FOR POSITIVE FLUID DISPLACEMENT [76] Inventor: Ernest Wildhaber, 124 Summit Dr.,

Brighton, NY. 14620 [22] Filed: Mar. 19, 1974 [21] Appl. No.: 452,508

Primary Examiner-.lohn .l. Vrablik [57] ABSTRACT The rotors of a pair have intersecting axes. Their intermeshing teeth have tooth numbers differing by one and are deep enough to contact all around the rotor periphery. The entire tooth surfaces of one rotor are formed conjugate to the tooth ends of the other rotor. Said tooth ends have convex profiles in planes perpendicular to the tooth direction. The curvature centers of said profiles are displaced from the pitch surface towards the tooth bottom, so that the tooth addendum is algebraically smaller than the curvature radius of said end profile. Preferably said tooth ends are applied to the larger rotor of the pair, and may have a constant profile all along the tooth length.

12 Claims, 13 Drawing Figures Pmmnnmw 3,856,440

SHEET 1 (IF 3 PATENTEU 3,856,440

sum 2 (LF 3 I PATENTEI] EH12 41974 sum 3 or 3 Hem] ROTOR PAIR FOR POSITIVE FLUID DISPLACEMENT The invention applies to compressors and motors for air or gaseous fluids and to pumps and motors for liquids. It relates to Rotary Positive Displacement Units described in my US. Pats. No. 3,236,186 granted Feb. 22, 1966 and No. 3,273,341 granted Sept. 20, 1966, and in my allowed patent application Ser. No. 331,781 filed Feb. 12, 1973, now US. Pat. No. 3,817,666 Reference is made to these disclosures. The invention can be considered an improvement thereof as regards the tooth shape of the rotors.

One object of the invention is to provide improved sealing of the contacting teeth. A further object is to provide continuous tooth profiles without break. Another aim is to provide a modified tooth shape that may be cut and ground with rotating cutters or grinding wheels cutting lengthwise of the teeth, using only depthwise feed. A further object is to lower production cost. These objects may be attained singly or in combination.

The invention will be described with reference to the drawings, in which FIG. 1 is a view of the tooth profile of the smaller rotor in a spherical surface centered at the intersection point of the rotor axes, looking along the instant axis and proportioned according to the invention. It is conjugate to the tooth top of the larger rotor.

FIG. 2 is a similar view of a tooth profile having addendum proportions according to known art.

FIG. 3 is an axial section of a rotor pair proportioned according to the invention, where the rotor with the basic tooth end is the smaller rotor of the pair, containing one tooth less than its mate. The teeth are shown in view rather than in section.

FIG. 4 is a similar axial section, where the rotor with the basic tooth end is the larger rotor of the pair, in accordance with the invention.

FIG. 5 is an axial section similar to FIG. 3, where however the basic tooth end has a constant profile all along the length of the teeth.

FIG. 6 is an axial section similar to FIG. 4, where the basic tooth end is on the larger rotor and has a constant profile all along the length of its straight teeth.

FIG. 7 is a view taken along the rotor axis, looking at the teeth of the larger rotor of the pair shown in FIG. 6.

FIG. 8 is a view taken along the curvature axis of the basic tooth end shown in FIG. 6.

FIG. 8a is an auxiliary diagram.

FIG. 9 is an axial section similar to FIG. 6, where however the basic tooth end is curved lengthwise and is a surface of revolution with a plane of symmetry containing the rotor axis.

FIG. 10 is also an axial section similar to FIG. 6, where however the teeth are curved lengthwise in a plane extending in peripheral direction, showing also a way of rotatably mounting the rotors.

FIG. 11 is a view of the smaller rotor of the pair shown in FIG. 10, taken along its axis and looking at the teeth.

FIG. 12 is a side view of the rotor pair of FIG. 10, at a larger scale.

In FIG. 1 20 and 21 denote the pitch circles of the rotor pair. They contact each other at the instant axis 22. The basic profile 23 at the tooth top of the larger rotor, with pitch circle 20, has a curvature center 24 at central point 27 Note that center 24 is displaced from pitch circle depthwise of the rotor teeth. The shown tooth addendum 22-27, of the larger rotor is here negative. More generally, the tooth addendum is algebraically smaller than the curvature radius 24-27,, and may be negative as shown.

The curvature center 24 describes a relative path 26 as the rotors run together, and the basic end-profile 23 envelops the tooth profile 27 of the smaller rotor. It should be noted that profile 27 is continuous and without breaks; and that the contact moves continuously in one direction through points 27 27 27 27,: during rotation in one direction. These points are shown on one side-profile only. They are symmetrical thereto on the opposite side. They are points of the sealing lines.

FIG. 2 shows the same instant axis 22 and pitch circles 20, 21, but here the curvature center 24 of the basic tooth-end profile 23 is displaced from the pitch surface and pitch circle 20 further away from the tooth bottom. Here the tooth addendum 22-27, is larger than the curvature radius 24'-27' The curvature center 24' describes a relative path 26. It has a loop 28 adjacent the tooth bottom of the smaller rotor. Accordingly the tooth profile 27' enveloped on the smaller rotor has a break at point 27,-. Contact between the basic end profile and profile 27' moves continuously from point 27, to 27' to 27 to 27, on uniform rotation of the rotors. And then, after an intermission without tangential contact, leaps to the opposite side, to the concave profile portion 27,, and then down to 27' in the central position.

The absence of break 27, in the design of FIG. 1 improves sealing and reduces leakage of fluid.

In gearing the concave profile portion below point 27,, FIG. 2, is called undercut. While some undercut is acceptable there, because of the ample clearance in gearing between the tooth tops and the tooth bottoms of the mating gears, undercut is more of a disadvantage on rotors where also the tooth bottom should be contacted, or almost contacted. The present invention avoids this undercut. It also facilitates production, as will be shown later on.

In FIGS. 3 and 4 the axes 30, 31 of the rotora intersect at 0 and include an obtuse angle with each other that differs from 180 by an angle s. The conical pitch surfaces of the two rotors roll on each other without sliding and contact one another along the instant axis of relative motion. Instant axis 32 includes a pitch angle p) with the axis of the larger rotor, and a pitch angle a== (90 p -s) with the axis of the smaller rotor.

FIG. 3 shows the basic tooth top t, to which the mating rotor is conjugate, on the smaller rotor. It may be part of a surface of revolution, or of a surface of like curvature at its midpoint. The axis 40 of said curvature surface is inclined at an angle b to the instant axis 32. In accordance with the invention it is shown displaced from the pitch surface towards the tooth bottom of the smaller rotor, and should be introduced as a negative amount in formula I below. In principal the basic tooth top portion could for instance be part of a conical surface with axis 40. Axis 40 itself lies on a conical surface about rotor axis 31, and appears in position 40' on the opposite side of the rotor axis. Here the tooth tops of the two rotors contact each other. 41' denotes the axis of the curvature surface at the tooth top of the mating larger rotor. The two axes 40', 41' include an angle b with each other. This angle depends on angle b in the manner described in US. Pat. No. 3,236,186 with a formula that can be transformed into tan b' sin c/cos p(ctn s tan p) sin c-cos c where c 2(s p) b What matters at any given distance from apex is the intersection of the curvature surface with a spherical surface about 0 at said distance from 0. Angle b may well vary with the distance from O in the above formula. It is seen then that the sum of the tooth-top curvature radii of the two rotors increases with increas ing negative b. This is made use of by the invention, as will be shown with FIG. 5.

FIG. 4 relates to a case novel with the present invention. Here the larger rotor with one more tooth has the basic tooth top. 41, is the axis of its curvature surface. It includes an angle b, with instant axis 32, shown negative. b is again the angle between the axes of curvature of the tooth tops when these contact in the plane of FIG. 4. Here the formula for b is:

tan b' sin c/c0s p(ctn s tan p) sin c"cos c where An important merit of placing the basic tooth top on the larger rotor lies in the production of its mate. Large rotary cutters and grinding wheels may embody the basic tooth top without interfering with the workpiece on the side opposite the generating engagement.

In designing the teeth, the angles b or b should be so selected that (b'b) or (bb,) is larger than zero and is comparable to b or b, respectively.

FIG. illustrates an embodiment where the basic tooth-top has a constant profile all along the tooth length, in planes perpendicular to the tooth direction. It is here applied to the smaller rotor, and is a cylindrical surface with axis 43. In this example the root lines 42, 42' of the mating teeth are conventional. They intersect apex 0 when extended. Angle b varies along the length of the teeth. It is determined as the angular distance between the intersection points of instant axis 32 and curvature axis 43 with a circle centered at 0. Angle b appears negative in FIG. 5 at all distances from O, increasing towards the small end of the teeth, to increase the angle b. This to obtain a more desirable curvature radius at the small end of the teeth of the larger rotor.

The following Figures all show the basic tooth-top applied to the larger rotor of the pair. The rotors shown in FIG. 6 have straight teeth extending along axial planes. The basic tooth-top 45 is a cylindrical surface with curvature axis 46. 47 denotes the instant axis. A sphere or ball 48 is interpoed between the rotors 50, 51, for the inner ends of the teeth to abut against. It is centered at O, the intersection point of the rotor axes. Sphere 48 may be rolled onto rotor 50in manufacture,

or cast onto it, or pressed onto it in a powder-metal operation of known type.

FIG. 7 is a view of the teeth of the larger rotor 50 shown in FIG. 6, looking along its axis 31. It shows the basic tooth tops 45.

FIG. 8 is a view at a larger scale, taken along the curvature axis 46 of the basic tooth top 45 of rotor 50 shown in FIG. 6. The inner or small end of the teeth is shown in dotted lines 53. The profile at end 45 is constant all along the tooth length in planes perpendicular to the tooth direction. These planes are here parallel to the drawing plane.

The tooth-top portions 45 shown in FIGS. 6 to 8 may be described by a broach in a rolling-generating motion, as if the two rotors were meshing together. The broach then makes one pass per tooth generated on the rotor blank 51.

The rotor pair shown in FIG. 9 differs from that shown in FIG. 6 by having teeth curved lengthwise. The basic tooth-top portion 56 of the larger rotor lies in a surface of revolution that has a plane of symmetry coinciding with the drawing plane, which contains the rotor axis 31. A portion 56 can be described with the cutting edges of a disk-type cutter that rotates on an axis perpendicular to said plane. Or a grinding wheel can be used in place of said cutter. Here also portion 56 has a constant profile in planes perpendicular to the tooth direction. 57 denotes the cutting path.

The rotor pair 61, 62 shown in FIGS. 10 and 11 also has teeth curved lengthwise. But here they are curved in a plane that extends peripherally of the teeth. The basic tooth-top portions 60 of rotor 61 can be described by cutting edges of a face-mill type cutter, or by a face-type grinding wheel, as their profile is constant all along the length of the teeth.

In the outlined production operations a tooth is generated in each feed cycle, which corresponds to a full turn of the tool head on the axis of the rotor it represents. To apply a cut all around the rotor it takes as many feed cycles as there are teeth in the rotor.

Instead of milling cutters, hobs may be used if desired, particularly face-type hobs in the embodiment of FIGS. 10! and 11. Hobs are timed to the rotation of the workpiece. The hob and workpiece are very slowly fed about the intersecting axes of the rotor pair, as they rotate in time with each other. Here a single feed cycle may complete the workpiece.

The constant-profile shape of the basic tooth top permits production of one rotor on existing machine-tools without or with little modifications. Production is efficient, and can be further accelerated by varying the feed rate. The mating rotor can be produced in a rolling operation with a master representing the rotor with the basic tooth top.

FIG. 8a shows a tool representing profile end 45. It may be a cutting tool cutting lengthwise of the teeth, or a grinding wheel. Its end-profile 45 gets into finishing contact between points 54, 54 during generation. The contact point moves from the mid-point, while cutting the tooth top of rotor 51, to point 54 as the cutting depth increases. It then reverses and returns to the midpoint when cutting at full depth; and moves to position 54 as the cutting depth decreases again, and back to the mid-point while cutting the tooth top of the follow ing tooth.

Profile 45 may be a circular arc, or a curve of the same curvature center 46 at its mid-point.

thenovel tooth shape with the different addendum proportion, according to the invention, decreases the angle between reversal points 54, 54'. This has important production advantages. A cutting tool is necessarily relieved back of the cutting faces for cutting clearance. A cutting profile appearing after repeated sharpening is shown in dotted lines 45' in FIG. 8a. Its distance from the full-line profile is a measure of the relief. To have sufficient cutting clearance at the points of reversal 54, 54', the distance between the curvature centers 46, 46' of the profiles 45, 45' has to be increased with increasing angle between points 54, 54. It easily reaches an excessive amount, that shortens cutter life. Also on a grinding wheel the amount of grinding stock available adjacent points 54, 54 decreases rapidly the closer the angle between said points approaches 180. This requires extra frequent dressing of the wheel and shortens wheel life. The invention keeps the angle between the end points 54, 54' within desirable limits.

FIG. 10 also indicates a way of rotatably mounting the rotors 61, 62 on their axes 63, 64 that intersect at O. Rotor 62 with the smaller tooth number is rigid with the drive shaft. It is mounted in a housing 65 by bearings 66, 67. Rotor 61 is mounted in housing cover 68 that is rigidly secured to housing 65. It is mounted on a bearing 69, and further by contact with a central sphere 70 engaged by rotor 62. The known fluid channels do not appear in this axial section.

FIG. 11 shows the cutting path 72 in the position when generating the tooth top 73 of rotor 62. In this position the portion 72 of the cutting path comes closest to the body of rotor 62 on the side opposite the generating engagement. The cutter diameter may be so chosen that portion 72' may dip into a tooth space of the rotor 62.

A larger-scale side view of the rotors 61, 62 is afforded by FIG. 12. Note the contact of the basic tooth top 60 all around the periphery. This indicates that very little torque is transmitted to rotor 61 by fluid pressure, so that its tooth sides are almost without load and require little lubrication.

In addition to the contact at the basic tooth top there is also contact between the sides of the teeth, as described in the named references. This contact is near the region of deepest penetration of the rotor bodies, adjacent the top of FIG. 12 and of the FIGS. showing axial sections.

All independent claims read on the embodiment of FIGS. 10 to 12.

While the invention has been described with several modifications, further changes may be made therein without departing from its spirit.

What I claim is:

l. A pair of rotors adapted to run on intersecting axes, having intermeshing teeth to provide fluid displacement and having tooth numbers differing by one tooth, said rotors having tooth-top portions of convex profiles in planes perpendicular to the tooth direction,

one rotor of said pair having its entire tooth surfaces fonned conjugate to the tooth-top portion of the other rotor,

the tooth addendum at mid-face of said other rotor being algebraically smaller than the curvature radius of its said profile at its mid-point, so that the curvature center is displaced from the pitch surface towards the tooth bottom.

2. A pair of rotors according to claim 1, wherein the teeth are straight, and each tooth extends along a plane containing the rotor axis.

3. A pair of rotors according to claim 1, wherein the teeth are curved lengthwise, the tooth-top portion of said other rotor being a surface of revolution that has a plane of symmetry containing the rotor axis.

4. A pair of rotors adapted to run on intersecting axes, having intermeshing teeth that extend inwardly from a spherical surface centered at the intersection of said axes, to provide fluid displacement, having tooth numbers differing by one tooth, said rotors having tooth-top portions of convex profile in a plane perpendicular to the tooth direction,

the rotor with the smaller tooth number having its entire tooth surfaces formed conjugate to the toothtop portion of the rotor with the larger tooth numher.

5. A pair of rotors according to claim 4, wherein the rotor with the larger tooth number has all-dedendum teeth without addendum at said spherical surface.

6. A pair of rotors according to claim 4, wherein the teeth are curved lengthwise.

7. A pair of rotors according to claim 6, wherein the curvature plane of the lengthwise curve of the rotor teeth extends peripherally of the teeth.

8. A pair or rotors adapted to run on intersecting axes, having intermeshing teeth to provide fluid displacement and having tooth numbers differing by one tooth, said rotors having tooth-top portions of convex profile in planes perpendicular to the tooth direction,

one rotor of said pair having its entire tooth surfaces formed conjugate to the tooth-top portions of the rotor,

said profiles of the last-named tooth-top portions being constant all along the length of the teeth on said other rotor.

9. A pair of rotors according to claim 8, wherein the proportion of tooth addendum to tooth depth changes lengthwise of the teeth.

10. A pair of rotors according to claim 8, wherein the extended face surface of the rotors bypasses the intersection point of the axes of said pair.

11. A pair of rotors according to claim 8, wherein the rotor with the larger tooth number contains the toothtop portions of constant profile.

12. A pair of rotors according to claim 8, wherein said constant profiles are circular arcs. 

1. A pair of rotors adapted to run on intersecting axes, having intermeshing teeth to provide fluid displacement and having tooth numbers differing by one tooth, said rotors having tooth-top portions of convex profiles in planes perpendicular to the tooth direction, one rotor of said pair having its entire tooth surfaces formed conjugate to the tooth-top portion of the other rotor, the tooth addendum at mid-face of said other rotor being algebraically smaller than the curvature radius of its said profile at its mid-point, so that the curvature center is displaced from the pitch surface towards the tooth bottom.
 2. A pair of rotors according to claim 1, wherein the teeth are straight, and each tooth extends along a plane containing the rotor axis.
 3. A pair of rotors according to claim 1, wherein the teeth are curved lengthwise, the tooth-top portion of said other rotor being a surface of revolution that has a plane of symmetry containing the rotor axis.
 4. A pair of rotors adapted to run on intersecting axes, having intermeshing teeth that extend inwardly from a spherical surface centered at the intersection of said axes, to provide fluid displacement, having tooth numbers differing by one tooth, said rotors having tooth-top portions of convex profile in a plane perpendicular to the tooth direction, the rotor with the smaller tooth number having its entire tooth surfaces formed conjugate to the tooth-top portion of the rotor with the larger tooth number.
 5. A pair of rotors according to claim 4, wherein the rotor with the larger tooth number has all-dedendum teeth without addendum at said spherical surface.
 6. A pair of rotors according to claim 4, wherein the teeth are curved lengthwise.
 7. A pair of rotors according to claim 6, wherein the curvature plane of the lengthwise curve of the rotor teeth extends peripherally of the teeth.
 8. A pair or rotors adapted to run on intersecting axes, having intermeshing teeth to provide fluid displacement and having tooth numbers differing by one tooth, said rotors having tooth-top portions of convex profile in planes perpendicular to the tooth direction, one rotor of said pair having its entire tooth surfaces formed conjugate to the tooth-top portions of the rotor, said profiles of the last-named tooth-top portions being constant all along the length of the teeth on said other rotor.
 9. A pair of rotors according to claim 8, wherein the proportion of tooth addendum to tooth depth changes lengthwise of the teeth.
 10. A pair of rotors according to claim 8, wherein the extended face surface of the rotors bypasses the intersection point of the axes of said pair.
 11. A pair of rotors according to claim 8, wherein the rotor with the larger tooth number contains the tooth-top portions of constant profile.
 12. A pair of rotors according to claim 8, wherein said constant profiles are circular arcs. 